Stock material or miscellaneous articles – Composite – Of polyamidoester
Patent
1983-12-29
1985-11-12
Anderson, Philip
Stock material or miscellaneous articles
Composite
Of polyamidoester
264129, 264255, 4284242, 4284244, B32B 2708
Patent
active
045528179
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an inactivated polyurethane and a method for preparing it.
Polyurethane (PUR) is generally manufactured by a reaction between polyfunctional isocyanates and alcohols. The finished product then has a certain residual isocyanate content. It has long been known that isocyanate molecules are toxic, this having restricted the use of polyurethane to fields where a certain isocyanate content has not been considered harmful.
An indication of the toxicity of isocyanate is that the hygienic limit value for its presence in the atmosphere (for instance in a workshop) is at present (in Sweden) as low as 0.01 ppm [ml (gas)/m.sup.2 (air)]. However, there is no limit value for the residual content of isocyanate monomers in completely cured polyurethane material, which may be attributable to the fact that no suitable method of analysis for detecting so low contents of isocyanate molecules as here contemplated has been elaborated.
The commonest symptom of exposure to isocyanate are allergic troubles in the form of irritations of the mucous membranes and the skin. Since the residual isocyanate monomer content of completely cured polyurethane is very low, it is possible nevertheless in many instances to use polyurethane in cases where the human body comes into contact with the material, if an air gap can be provided between the polyurethane and the body. One example of this is the use as padding in mattresses which are covered with a fabric.
Considering the other properties of polyurethane, it would also serve well in other products, but its use has hitherto been hampered to a great extent by its noxiousness to the skin and the mucous membranes.
The object of the present invention therefore is to provide an inactivated polyurethane which can also be used in such products as will come into direct contact with the skin, such as ear protectors or dressing materials, e.g. plaster.
This object is achieved by coating polyurethane with a layer of a polymer which contains functional groups capable of reacting with isocyanate. Free isocyanate groups leaving the polyurethane material will then be prevented not only mechanically from escaping out into the ambient atmosphere but will react with the alcohol groups in the polymer layer and be chemically bound therein.
Examples of preferred functional groups which are capable of reacting with isocyanate are hydroxyl groups.
The coating of the polyurethane can be carried out in various ways. Thus, the polyurethane can first be molded to the desired shape and thereafter be coated with a thin layer of a suitable polymer which then reacts with isocyanate groups in the polyurethane.
Another mode of producing the coating is first to apply a thin layer of a suitable polymer to the inner side of the mold in which the polyurethane is to be shaped, and then form the polyurethane in the mold. Functional groups in the polymer will then react with isocyanate groups in the polyurethane, whereby the layer of polymer is chemically bonded to the polyurethane.
A suitable hydroxyl group containing polymer is e.g. polyvinyl alcohol, but other hydroxyl group containing polymers may also be used, such as partly hydrolyzed polyvinyl acetate or copolymers containing vinyl alcohol or hydrolyzed polyvinyl acetate, polymers prepared from vinyl and acrylate monomers containing hydroxyl groups, or hydroxyl group-terminated low molecular polyesters.
For a more detailed illustration of the invention, reference is now had to the following Example which is however not meant in any way to restrict the scope of the present invention.
EXAMPLE
Since the isocyanate content of polyurethane is so low that it cannot be analyzed by conventional methods, a model test has been conducted in order to illustrate the penetration of the isocyanate molecule through polyvinyl alcohol.
A mixture of toluene-2,4-diisocyanate (2,4-TDI) and toluene-2,6-diisocyanate (2,6-TDI), which are common starting materials for the preparation of polyurethane, was batched in a test tube over which the sheeting to be examin
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patent: 4294880 (1981-10-01), Nishida
patent: 4331735 (1982-05-01), Shanoski
patent: 4389454 (1983-06-01), Horacek et al.
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Anderson Philip
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